import jakarta.servlet.ServletContext;
import jakarta.servlet.annotation.WebListener;
import jakarta.servlet.http.HttpSessionEvent;
import jakarta.servlet.http.HttpSessionListener;

@WebListener
public class MyListener implements HttpSessionListener {

    public void sessionCreated(HttpSessionEvent se ) {
       int online = 0;

       ServletContext context = se.getSession().getServletContext();
       if(context.getAttribute("ol") == null) {
           online = online + 1;
           context.setAttribute("ol", online);
       } else {
           online = (int) context.getAttribute("ol");
           online = online + 1;
           context.setAttribute("ol", online);
       }
    }

    public void sessionDestroyed(HttpSessionEvent se) {
           ServletContext context = se.getSession().getServletContext();
           int online = (int) context.getAttribute("ol");
           online = online - 1;
           context.setAttribute("ol", online);

    }
}
